(European Wand Loosestrife) Lythrum Salicaria L

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MN NWAC Risk Common Name Latin Name Assessment Worksheet (04-2011) Purple loosestrife Lythrum salicaria L.

(European wand loosestrife) (Lythrum virgatum L.)

Photo: J.Rendall, MN DNR Reviewer Affiliation/Organization Date (mm/dd/yyyy) Laura Van Riper Minnesota Department of Natural 08/13/2013 Resources

Note: Lythrum virgatum L. (European want loosestrife), is accepted by the Integrated Taxonomic Information System (www.itis.gov) and USDA Plants (http://plants.usda.gov/java/profile?symbol=LYVI3) (both accessed 3-22-2013) as a distinct species from Lythrum salicaria (purple loosestrife). However, L. salicaria and L. virgatum interbreed freely, differ in few diagnostic characteristics, are difficult for inspectors to distinguish when plants are vegetative, and were previously considered by many taxonomists to be the same (Rendall 1989, Anderson and Ascher 1993, Lindgren and Clay 1993). Therefore, while the data in the risk assessment relates to L. salicaria unless otherwise noted, the results of this risk assessment will apply to both L. salicaria and L. virgatum.

Box Question Answer Outcome 1 Is the plant species or genotype non-native? Yes. Non-native to Minnesota. Native to Europe and Go to Box 3 Asia (Thompson et al. 1987). 3 Is the plant species, or a related species, Yes. Listed as a noxious weed in 33 states Go to Box 6. documented as being a problem elsewhere? (http://plants.usda.gov/java/profile?symbol=LYSA2). 6 Does the plant species have the capacity to establish and survive in Minnesota?

Box Question Answer Outcome A. Is the plant, or a close relative, currently Yes, it is recorded in most counties in Minnesota. Go to Box 7. established in Minnesota?

Recorded purple loosestrife populations in Minnesota as of December 2012 (Invasive Species Program 2012). 7 Does the plant species have the potential to reproduce and spread in Minnesota? A. Does the plant reproduce by Significant clonal growth has not been found (Thompson et Yes, Go to 7B asexual/vegetative means? al. 1987), but there is localized clonal growth with annual No, Go to 7C shoots produced each spring from overwintering, spreading root buds (Mal et al. 1992). If pieces of the root crown are spread to new sites (such as through movement of soil), the plants could establish. B. Are the asexual propagules effectively If pieces of the root crown are spread to new sites (such as Yes, Go to 7I dispersed to new areas? through movement of soil), the plants could establish. The No, Go to 7C spread of purple loosestrife is primarily by seeds and germinated seedlings (Thompson et al. 1987, Skinner et al. 1994). C. Does the plant produce large amounts of Yes. Seed production of 2.7 million seeds per plant has been Go to 7F viable, cold-hardy seeds? reported (Thompson et al. 1987). Welling and Becker (1990) reported an extensive seed bank of 410,000 seeds/m2 in the top 5 cm of soil.

Box Question Answer Outcome F. Are sexual propagules – viable seeds – Yes. Means of dispersal likely largely by floating seedlings Go to 7I effectively dispersed to new areas? and ungerminated seeds. Also likely to spread in mud adhering to wildlife, livestock, treads of vehicles, equipment, and other activities that move soil. May spread by ingestion of seeds by birds. (Thompson et a. 1987) Seeds may also spread by wind (Mal et al. 1992), particularly during the winter. I. Do natural controls exist, species native to No, there are not native controls. Go to Box 8 Minnesota, that are documented to effectively Surveys conducted in the northeastern US found 59 prevent the spread of the plant in question? species of phytophagus insects on purple loosestrife, but none reduced populations or caused appreciable damage (Hight 1990). There are now widely distributed introduced (non- native) biocontrol insects (Galerucella calmariensis and Galerucella pusilla that are providing some control (Invasive Species Program 2012). 8 Does the plant species pose significant Listed below are studies related to the impacts of purple Yes, go to Box 9. human or livestock concerns or has the loosestrife. In addition to these studies, there are review No, then no regulation. potential to significantly harm agricultural papers that question these studies and propose that the production, native ecosystems, or managed data on purple loosestrife is inconclusive (Hager and landscapes? McCoy 1998, Farnswoth and Ellis 2001, Lavoie 2010). A. Does the plant have toxic qualities, or No information found on purple loosestrife as a risk to other detrimental qualities, that pose a livestock or people. significant risk to livestock, wildlife, or Blossey et al. (2001) cite a number of studies relating to people? reduction of high quality bird habitat due to purple loosestrife (Rawinski and Maleki 1984, Whitt et al. 1999, Hickey 1997, Hickey and Malecki 1997, Lor 2000). Studies have found a reduction in the development and survival rate of American toad (Bufo americanus) tadpoles due to purple loosestrife (Maerz et al 2005, Brown et al 2006). Lavoie (2010) (Table 3) cites 10 studies of impacts of purple loosestrife on bird species; 4 showed negative impacts, 1 showed positive impact, and 5 had no impact. 3

Box Question Answer Outcome B. Does, or could, the plant cause significant When purple loosestrife is present in pastures it has been financial losses associated with decreased found to reduce the forage value to livestock (Thompson et yields, reduced crop quality, or increased al. 1987). No reports of significant financial losses to crops production costs? were found. C. Can the plant aggressively displace native Yes. species through competition (including Blossey et al. (2001) cite a number of studies relating to allelopathic effects)? displacement of native species and reduction in plant biodiversity, including: • Reduction in native plant species (Gabor et al. 1996) • Domination of seed bank (Welling and Becker 1990) • Superior competitive ability of purple loosestrife (Weiher et al. 1996) • Replacement of cattail (Typha) (Mal et al. 1996, Mal et al. 1997, Weiher et al. 1996, Weihe and Neely 1997) • Reduction in pollination and seed set of native plant Lythrum alatum (Brown 1999) Lavoie (2010) (Table 3) cites 20 studies of impacts of purple loosestrife on plant species; 8 showed negative impacts, 7 had no impact, 4 had null or negative impacts, and 1 had null or positive impacts.

Box Question Answer Outcome D. Can the plant hybridize with native Lythrum alatum (winged loosestrife) is native to species resulting in a modified gene pool and Minnesota. potentially negative impacts on native Anderson and Ascher (1993) note that: populations? “Despite ploidy differences, purple loosestrife (4x and 6x) and L. alatum (2x) will intercross in natural settings (Levin, 1970)” and “Cultivars derived from interspecific hybridization between purple loosestrife and L. alatum (Table 1)—e.g., ‘Columbia Pink’, ‘Morden Gleam’, dwarf forms of ‘Robert’, and ‘Morden Rose’— could serve as hybrid bridges for the transfer of evolutionarily adaptive traits from North American species into weedy Eurasian taxa.” E. Does the plant have the potential to Blossey et al. (2001) cite a number of studies relating to change native ecosystems (adds a vegetative alteration of wetland function, including: layer, affects ground or surface water levels, • Changes in decomposition rates and timing etc.)? (Barlocher and Biddiscombe 1996, Emery and Perry 1996, Grout et al. 1997) • Changes in porewater cheminstry (reduced P) (Templer et al. 1998) Lavoie (2010) (Table 3) cites 10 studies of impacts of purple loosestrife on ecosystem processes; 4 showed negative impacts, 2 had no impact, and 4did not clearly state the impacts. F. Does the plant have the potential to No reports of this were found. introduce or harbor another pest or serve as an alternate host? 9 Does the plant species have clearly defined benefits that outweigh associated negative impacts? A. Is the plant currently being used or No. Lythrum salicaria and Lythrum virgatum are Go to Box 10 produced and/or sold in Minnesota or native prohibited noxious weeds on the control list and to Minnesota? therefore producing or selling plants is prohibited.

Box Question Answer Outcome 10 Should the plant species be enforced as a noxious weed to prevent introduction &/or dispersal; designate as prohibited or restricted? A. Is the plant currently established in Yes (Invasive Species Program 2012). Go to Box 10B. Minnesota? B. Does the plant pose a serious human No. Go to Box 10C. health threat?

Box Question Answer Outcome C. Can the plant be reliably eradicated Plant cannot be reliably eradicated (entire plant) on a Yes (control feasible), but (entire plant) or controlled (top growth only statewide basis using existing practices and available eradication not feasible, to prevent pollen dispersal and seed resource. then the recommendation production as appropriate) on a statewide is Prohibited Noxious basis using existing practices and available Plant can be controlled (reduction of seed production) Weed Control list with resources? by biological control insects. Biocontrol insects reduce biocontrol as an populations of purple loosestrife, but do not prevent all acceptable method of seed production. control.

If more complete control of seed production is required OR than is provided by biocontrol insects (such as mowing or herbicide), then the plant cannot be reliably No (control not feasible controlled on a statewide basis using existing practices on a statewide basis), then and available resources. the recommendation is Restricted Noxious Weed. Biological control: Four species of insects, two leaf- eating beetles, Galerucella calmariensis and G. pusilla; OR a root-boring weevil, Hylobius transversovittatus; and a flower-feeding weevil, Nanophyes marmoratus, have New case: The plant has been released as potential biological controls for had an extensive, active loosestrife in Minnesota (Invasive Species Program biological program and 2012). The Galerucella species are widely distributed the biocontrol insects are in the state (Invasive Species Program 2012). considered widely Biological control may be the main way by which distributed in Minnesota purple loosestrife could be controlled on a statewide and effective at reducing basis. The questions to consider are whether biocontrol populations. Therefore, agents are already widely established in the state and the the recommendation is to efficacy of those biocontrol agents. If biocontrol agents make purple loosestrife a are considered to be widely distributed and effective, restricted noxious weed to then perhaps the Restricted Noxious Weed category prevent new introductions, (prevent transport and sale that can cause new but expect that the widely introduction) is sufficient. distributed biocontrol insects will provide control.

Box Question Answer Outcome

Final Results of Risk Assessment Review Entity Comments Outcome NWAC Listing Subcommittee First review – 06/20/2013, Final Review 08/12/2013 List as a Restricted This species was discussed in great length as to the Noxious Weed validity of continued listing as a Prohibited Noxious Weed. Although counties and townships commented that not many enforcement issues occur for purple loosestrife on private lands, it still remains an issue in wet ditches and private lands adjoining public waterways.

The issue of biological control agents was discussed and there was concern that moving to the Restricted List would decrease the efficacy of the biocontrol program statewide. That said, the recommendation went through to the full committee to consider reclassifying as a Restricted Noxious Weed. NWAC Full-group Reviewed 12/28/2013. Many members of the group Vote 3 - 9 to rejecting the voiced concern over reclassification of this species. Listing Subcommittee’s Successful biocontrol releases and the advent of cost recommendation and to efficient and more effective herbicides. Several member continue listing as a representatives mentioned that they felt both biological Prohibited-Control controls and herbicide treatments effectively manage Species purple loosestrife when and where it becomes problematic. MDA Commissioner Reviewed 02_24/2014 Accepted NWAC’s Recommendation to remain as a Prohibited- Control species File # MDARA00030PULOS_2_24_2014 Prohibited-Control Noxious Weed

References:

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